In recent years, a variety of nanostructures such as nanocarbons, nanofibers, and nanowires have been attracting attention as materials excellent in various characteristics such as mechanical characteristics. Of these, nanocarbons and especially fibrous carbon nanostructures such as carbon nanotubes (hereafter also referred to as “CNTs”) have been attracting attention as materials excellent in electrical conductivity, thermal conductivity, and mechanical characteristics.
However, nanostructures such as CNTs are fine structures with diameters in nanometer size, and therefore are poor in handleability and processability when used alone. Hence, a plurality of nanostructures are combined into an aggregate in film form as an example, or nanostructures are compound with a polymer material such as resin or rubber or metal to form a composite material. The resultant aggregate or composite material is then put to various uses. As a method of forming an aggregate of nanostructures, a method of removing, from a nanostructure dispersion liquid obtained by dispersing nanostructures in a dispersion medium, the dispersion medium has been proposed. As a method of forming a composite material including nanostructures, a method of precipitating or depositing, from a composite material composition obtained by mixing a matrix material such as a polymer material and a nanostructure dispersion liquid, a composite material has been proposed.
To achieve excellent characteristics of an aggregate of nanostructures or a composite material, there has been demand for a dispersion liquid obtained by favorably dispersing nanostructures in a dispersion medium, as a nanostructure dispersion liquid used to form an aggregate or a composite material. As a method of producing a nanostructure dispersion liquid, for example, a method of dispersing nanostructures in a dispersion medium using an ultrasonic homogenizer, a jet mill, or the like has been proposed (for example, see PTL 1 to PTL 4).